First in situ determination of ground and borehole thermal properties in Latin America

Abstract

The design of a ground heat exchanger for Underground Thermal Energy Storage (UTES) applications requires, among other parameters, knowledge of the thermal properties of the soil (thermal conductivity, borehole thermal resistance and undisturbed soil temperature). In situ determination of these properties can be done by installing a vertical borehole heat exchanger (BHE) and performing the so-called thermal response test (TRT). The present paper describes the results of a cooperative work between research groups of Chile and Argentina, which led to the first thermal response test performed in Latin America. A setup for implementing the TRT was prepared at the “Solar Energy Laboratory” of the Technical University Federico Santa Maria, Valparaiso, Chile. The test was realized over 9 days (24 June to 3 July 2003) while inlet and outlet fluid temperatures of the BHE and the ambient temperature were measured every minute. A comparison between conventional slope determination method, Geothermal Properties Measurement (GPM) data evaluation software based on numerical solutions to the differential equations governing the heat transfer processes and two variable-parameter fitting was performed in order to calculate the thermal conductivity and borehole thermal resistance. The detailed study of ground properties in different regions of Chile and Latin America (Argentina, Brazil) is a good precondition for future investigation and application of the Borehole Thermal Energy Storage (BTES) technology in the region.